The present invention relates generally to integrated optic waveguide switch arrays and optical cross-connect networks that contain microelectromechanical system (MEMS) microstructures/actuators and micromachined optical waveguide networks on planar lightwave circuits (PLCs) and it is directed particularly to reconfigurable and scalable all-optical switching for computer systems and telecommunication networks. The invention is specifically disclosed as a Micro-Opto-Electro-Mechanical System (MOEMS) that fabricates MEMS actuators and high-bandwidth PLCs by using well-established lithographic batch processing techniques and subsequently assembles them into integrated optic waveguide switches or optical cross-connect networks.
Recently there has been an accelerated integration of computer systems and communication networks in an attempt to satisfy the ever-increasing information processing, transmission, and distribution needs for future computer systems and communication networks. High-performance microprocessors with large integration density, diverse functionality, and high-speed operation capabilities are now in widespread use due to innovative architecture designs and improved silicon fabrication processes. Similarly there has been an increasing demand for better performance in network computing. Over the past several years, the rapidly increasing traffic volume carried by telecommunication networks clearly has been observed, and this is a result of wider use of bandwidth-intensive applications such as Internet access, electronic commerce, multimedia applications, and distributed computing. In accommodating this demand, optical telecommunication systems employing optical fibers as the transmission medium have exhibited a superior performance/cost ratio for both long-haul and short-haul routes to than any other type of telecommunication systems. In particular the emerging dense wavelength-division multiplexing (DWDM) and all-optical network communication systems have shown some promising and exciting potentials. However there still exists a need to improve delay, bandwidth, and connectivity of optical telecommunication networks, as the information system""s subscriber growth continues unrestrained.
Although fiber optic cables for both long-haul and short-haul routes increasingly have been deployed by telecommunication service providers, the ever-increasing network traffic has created some constraints on communication network in terms of speed, capacity, and connectivity of networks. Telecommunication service providers have addressed these speed, capacity and connectivity constraints by either installing new fiber cables or by expanding the transmission capacity using faster devices or DWDM techniques. While timedivision multiplexing (TDM) increases the transmission speed of optical signals, DWDM increases the number of optical signals, called channels, transmitted simultaneously on a single fiber and it is ideal for high volume point-to-point or backbone links with minimal switching and routing requirements. However, in the emerging DWDM metropolitan and local area networks, the primary concern is not the network capacity but the network connectivity through reconfigurable switching. Regardless of the method used for addressing capacity constraints, the a fiber optic switching will become a major issue for optical telecommunication systems. Since the fiber optic telecommunication technology first became available, many network managers have preferred all-optical networks for benefits in terms of bandwidth, security, and segment length. Optical cross-connect networks can also improve the efficiency of all-optical networks by providing a bit-rate independent and format independent network switching. Without the all-optical networks, the signals of traditional optical telecommunication networks first must be converted from optical to electrical form at switching ports and the routing information in the information packet analyzed and utilized for proper signal routing. Then the signal must be converted to the optical form for a subsequent signal routing and transmission. These optical-to-electrical and optical-toelectrical signal form conversions reduce the overall network efficiencies as it introduces delays and noise.
It is widely believed that the DWDM network is an enabling technology for Internet applications, as the expectations of the Internet""s great potential will not be realized without the bandwidth gain provide by DWDM. Direct fiber optic switching without electrical-to-optical or optical-to-electrical conversions is much needed for the all-optical DWDM network. The unprecedented record of growth being generated by Internet traffic and tremendous amount of data being dumped on the public network show no sign of slowing yet. Without optical telecommunication network and optical fiber""s seemingly unlimited bandwidth potential as the fundamental transmission technology, the Internet performance will be significantly slowed as the subscriber growth increases unrestrained. Notably there is a need for fiber optic switches for all-optical DWDM networks, which can provide low cost, small crosstalk, reliable, compact, reconfigurable, modular, scalable, and wavelength/polarization insensitive characteristics.
Accordingly, it is a primary objective of the present invention to provide Micro-Opto-Electro-Mechanical System (MOEMS) for integrated optic waveguide switches and optical cross-connect networks. The MOEMS can deliver low cost, small crosstalk, reliable, compact, modular, scalable, and wavelength/polarization insensitive all-optical switching capabilities by integrating microelectromechanical system (MEMS) actuators and micromachined planar lightwave circuit (PLC) networks.
It is another objective of the present invention to provide a method of constructing integrated optic waveguide switches for two-input/two-output crossbar switching such that it allows a seamless integration of MEMS actuators and micromachined PLCs at the micro scale.
It is yet another objective of the present invention to provide a method of constructing integrated optic waveguide two-input/two-output crossbar switches for an Add/Drop switch and of Add/Drop switch applications.
Another objective of the present invention is to provide a method of constructing reconfigurable, non-blocking, and scalable optical cross-connect switches by using integrated optic waveguide switch arrays and PLC routing networks on MOEMS, which utilizes the inherent MOEMS characteristics: miniaturization, multiplicity, and micro-optoelectronics.
It is a further objective of the present invention to provide a method of constructing multifunction MEMS vertical mirror/filter actuators for DWDM Add/Drop filter and multiplexer applications, which combines out-of-plane vertical mirror or multi-layer thin-film filter plates on MEMS actuators.
It is yet a further objective of the present invention to provide a method of constructing tapered, off-set, and anti-reflection X-crossing boundary conditions for optical waveguide networks as well as providing parallel and non-parallel vertical movable plates in order to reduce insertion losses and to equalize optical signal powers.
It is yet another further objective of the present invention to provide a method of constructing a low power MEMS actuator, which exhibits zero-static power consumption.
Additional objectives, advantages and other novel features of the invention will be set forth in part in the description that follows and in part will become apparent to those skilled in the art upon examination of the following or may be learned with the practice of the invention.
To achieve the foregoing and other objectives, and in accordance with one aspect of the present invention, improved Micro-Opto-Electro-Mechanical Systems (MOEMS) are provided to support the seamless and scalable integration of MEMS actuators and PLCs. Such MOEMS can integrate high-bandwidth waveguide networks of PLCs and miniaturized MEMS microstructures/actuators into a single module.
Some of the essential components for optical communication system are devices that have branching, switching, filtering, and wavelength multiplexing functions. Until recently the majority of these were fabricated using optical fibers or bulk optics, both of which exhibit inherent limitation in size, speed, and large-scale integration capability. To overcome these limitations, many groups around the world have pursued research on planar waveguide network, such as planar lightwave circuits (PLCs) and silicon optical bench (SOB). These names came from the planar geometry of the waveguide circuits and the use of waveguide chips to attach other optoelectronic components. The PLCs have reached a level of development to produce a commercial component that can compete and surpass fiber-optic or bulk-optic components. The silica glass integrated waveguide circuits, made from glass composition similar to that of optical fibers, have shown many benefits such as low transmission losses, direct and low-loss interfacing to optical fibers, and a capability to integrate various devices into a single substrate, such as directional couplers, filters, splitters, combiners, star couplers, multiplexers, demultiplexers, and switches.
Through the use of MOEMS device structures presented in the current invention, a low cost, small crosstalk, reliable, compact, reconfigurable, modular, scalable, and wavelength/polarization insensitive integrated optic waveguide switch array can be fabricated in a lithographic batch process using well-established integrated circuit (IC) fabrication processes. The integrated optic waveguide switch is an integrated hybrid microsystem: MOEMS, which is capable of providing all-optical switching within a PLC platform through the aid of MEMS microstructures/actuators. By combining MEMS actuators (vertical mirror actuators) and micromachined PLCs into a single structure, the normally passive PLC can actively switch optical signals and reconfigure the PLC network connectivity. The integrated optic waveguide switch can utilize a vertical mirror actuator fabricated by a deep silicon reactive ion etch (RIE) process to provide many unique benefits such as scalability, low cost, small crosstalk, compactness, and wavelength/polarization insensitivity. In a current technology, the conventional fiber optic switches require assembly and alignment of multiple optical fibers. The current packaging process for optical fibers and other alignment structures inevitably incurs a non-uniform device performance and a large-scale array expansion of fiber switch is difficult to implement due to a discrete device configuration. Since the integrated optic waveguide switch utilizes lithographically defined integrated optic waveguide network and MEMS actuators as well as simple and single-step packaging processes, it is ideally suited for large-scale fiber switching applications involving an array of input/output fiber ports. The present invention""s unique device structure and packaging process renders a simple and single-step alignment operation between vertical mirror actuators and integrated optic waveguides regardless of the number and location of optical switches on the MOEMS platform. This feature is particularly useful to implement the scalable and reconfigurable all-optical communication networks at low cost.
In the emerging DWDM metropolitan and local area networks, the major concern is not the network capacity but the network connectivity. Through its switching capability, an optical Add/Drop switch can either add or drop communicating nodes of telecommunication network systems as the needs for network connectivity change. The number of active nodes in local area network can be dynamically increased or decreased depending on network traffic volume, fairness and priority of individual communicating nodes and so on. Besides the optical Add/Drop switches, the optical cross-connect switch array is another indispensable component for optical communication systems. It can switch and transmit optical signals directly between any input/output ports in both analog and digital formats and in a mixture of multiple data rates without electrical-to-optical or optical-to-electrical signal conversions. Due to the property that photons do not directly interact with each other in contrast with electrons, an optical cross-connect switch can be implemented on a single interconnect layer of PLC by using a planar X-crossing waveguide structure. It is possible to construct a strictly non-blocking cross-connect optical switch array on MOEMS platform by using many popular multistage network structures such as Benes, Omega networks and so on.
The power consumption and multi-functionality of MEMS devices are very important features to allow MOEMS expand and create a large-scale smart microsystem. Small power consumption of MEMS actuator allows a less demanding requirement for power management and device packaging and, subsequently, it facilitates a dense integration of integrated optic waveguide switch array. In general, device power consumption can be classified into dynamic and static power consumption. While it is impossible to eliminate dynamic power consumption, many devices for computer systems and communication networks can achieve zero or near-zero static power consumption as seen in CMOS circuits for VLSI systems. In the present MOEMS invention, an innovative locking mechanism can provide a method of constructing a low power MEMS vertical mirror actuator, which exhibits zero-static power consumption. After a dynamic reconfiguration of switch networks, the Add/Drop switch and cross-connect switch array would not consume any static power due to the use of MEMS lock actuators. It is also possible to implement vertical mirror actuators by using MEMS micro-grippers on linear comb drivers, where the micro-grippers holding vertical mirrors can provide a switching movement through a use of electrostatic comb drivers. By inserting vertical micro mirror or multi-layer thin film filter plates into the micro-grippers, it is possible to accomplish optical signal reflection as well as DWDM channel Add/Drop filtering. The multifunctional MEMS vertical mirror/filter actuator will enhance the functionality and reconfigurability of emerging DWDM metropolitan and local area networks.
Still other objective of the present invention will become apparent to those skilled in this art from the following description and drawings wherein there is described and shown a preferred embodiment of this invention in one of the best modes contemplated for carrying out the invention. As will be realized, the invention is capable of other different embodiments, and its several details are capable of modification in various, obvious aspects all without departing from the invention. Accordingly, the drawings and descriptions should be regarded as illustrative in nature and not as restrictive.